how to find separation between antenna

Ejem.
Using the info you are providing its's more or less 46.5 billion light-years (the radius of the observable universe)
Seriously. Try to be be more precise: application, frequency, etc...
Good luck

Minimum 20dB is a good number in antenna separation. This isolation is fine for getting at least minimum performances for diversity or for a two-antenna duplex system.

suppose frequency of operation is 20GHz. then how to find the separation between antennas ex dipole antenna?
sum paper i reffered that it should be greater then lamda..is it true r not i don't know

plz help

Yes, distance greater than λ is fine, but is good to look also for isolation in dB at operating frequency to eliminate any kind of interaction between antennas.

http://www.cisco.com/en/US/tech/tk72...8019f646.shtml

above link gives the distance of separation between antenas

in this link it says that
The 2.4 GHz wavelength is approximately 4.92 inches. Therefore, to support diversity on a 2.4 GHz radio with two separate antennas, the antennas should be spaced approximately 5 inches apart. The antenna pair could also be spaced at multiples of 5 inches, but the distance between should not exceed 4 multiples: reflected waves farther apart than that are likely to be so distorted and different in delay spread that the radio could not work with them.

how did he got 4.92 inches?

plz help

@ashokone,
Did you calculated for λ pls?
K.

i am not getting how he was represented the wavelength in inches?

anyone have an idea regarding this plz help

Use your very, very elementary equations. lambda=c/f. Then convert that to inches.

i did already, getting lamda=0.125 and if we convert it into inches multiply it by 2.54

gives the lamda in inches=0.3175 is the answer i am getting

Uh, that's not correct. Inches -> cm is *2.54. cm -> inches is /2.54.